DRIVE SHAFT COMPONENTS
TYPICAL FAILURE RELATED TO A BROKEN PART
Most of the failures are the result of shock loads. It causes parts of the driveline to break. Shock loads may occur during following cases:
- Frequently engaging and disengaging of the clutch.
- Sudden engagement of spinning tires with the ground.
- While reversing into a heavy trailer or pulling away from it with breaks of trailer engaged.
- Shock loads are caused due to contact of mating yokes. Mating yokes may come in contact during suspension due to improper operating angles. Yoke with suitable angle should be used to avoid this.
- Excessive torque through the yoke. It can be avoided by using yokes having higher torque rating.
Tube yoke fracture
- Improper welding can cause tube yoke failures. The tube yoke circle welds should be started in line with the tube yoke ear and 180 degrees from the tube weld seam.
Slip yoke fractures
Slip yokes usually crack near the end of the spline, when the drive shaft slip is not installed properly.
- The drive shafts must operate at mid-slip. If failure occurs however the length of the pipe must be changed.
End yoke fractures
- End yoke sometimes fracture near the tangs, it may be a result of improper bearing strap bolt torque or improper handling.
To avoid this failure the U-joint bearing must not rotate in the bearing pocket, the rotation of bearings may cause excessive wear. Wear causes misalignment and vibrations which may lead to fracture of the tangs.
A properly installed beating strap holds the bearing tight in its place and avoids rotation. When the bearing straps are installed they stretch and thus a proper torque is established. The stretching causes the bearing strap to be non reusable.
Premature center bearing or pillow block failures
Center bearing and/or center bearing rubber failure
Secondary couple loads are the main cause of Center Bearing or Pillow Block failure. Secondary couple loads generate when the operating angle at the front end of a coupling shaft are large and occur twice per revolution. The force generated travels down the centerline of the driveshaft and creates a bending on the drive shaft. Since the drive shaft is bolted fast on the driver and driven end, it tries to bend the driveshaft at the connecting points. Since the components cannot be bent the bearing and the surfaces attached to it are loaded. This causes the bearing rubber to fail.
To avoid this type of failure the operating angle at drive end of the drive shaft must always be less than 1 and half degrees.
There should be regular inspection of the center bearing to see if the bearing is wearing out, which is typically depicted by black rubber dust near the bearing surface. If the bearing is showing signs of wear the operating angle needs to be checked and rectified.
Center bearing failures related to weight
Center bearings may also fail under the heavy weight of a drive shaft. Heavy duty drive shafts with thick walled tubes can cause the slotted rubber cushions of center bearing to collapse under load. Thus heavy duty drive shafts must have solid rubber cushion design with sufficient stiffness to withhold the weight of the drive shaft.
Drive Shaft Tubing
- This failure is usually the result of shock load. The shock load might occur due to the popping of the clutch or sudden engagement of spinning tires with the ground
This type of failure is generally a fatigue type failure. a crack occurs in the tube weld circle and the progress around the tube.
To avoid this kind of failure the tube weld seam must be kept in line of the yoke ear and the welding of the seam must be started 180 degrees from the tube weld seam.
A high operating angle which generates large torsional vibrations are also the cause of fractured tubing's. U-joint operating angle should always be less than 3 degrees.
Welding of the balance weight can also cause failure of drive shaft tubing. Welding of balanced weights near the tube weld seam or near the circle weld can cause the metallurgical structure to change and thus lead to premature fatigue failure. thus balance weights should never be welded over the tube weld seam or near the circle weld of the tube yoke.
Tubing also fails at its critical speed. A drive shaft which is too long with respect to its operating speed may show this kind of failure. the critical speed must be calculated and should always be more than its maximum operating speed.
U Joint (TYPICAL UNIVERSAL JOINT KIT FAILURES)
When the needle marks get embossed on the bearing surface of the U-joint it is known as Brinelling. The main causes are excessive continuous torque loads, excessive driveline operating angle, seized slip yoke splines, bent yoke and over tight U-bolts. Torque to be transmitted by the drive shaft should be calculated and a U-joint should be used according to it.
When the surface of the bearing has been worn out and it looks like a layer of material have been removed from the surface it is known as Spalling. The main causes of Spalling are contamination of the bearing with water, unsuitable lube type or lubrication failure.
Burned U-joint cross
When a bearing operates under insufficient lubricant it causes the trunnions to be burnt. This may occur when sufficient purging is not achieved in the bearing. Improper application or a use of wrong lube type can also cause burnt U-Joint cross. To avoid such cases recommended purging should be achieved at all the 4 u-joint seal. Recommended lube type should be used.
When the end of the trunnion looks as if material has been carved out of it, it is known as end galling. This may occur due to high u-joint operating angle, bent yoke or improper lubrication. To avoid this the operating angles must be kept below 3 degrees.
Ujoint fractures may be a result of shock loads, excessive torque loads or a result of improper application. It can be avoided by using U-Joint suitable to the series of the driveline.